What app can I use for quick chat with my users?

Ive just moved all the Kanji Koohii feedback to Github's Issue system here. (anyone motivated just get to the README file and you' ll find the bleeding edge site =))

Now I realize I need a very simple CHAT GROUP kind of app or site so I can send some tests to people and ask how it works on their device.

This would complete the issue system very well .

Needs:

- chat log so people don't need to reply in real time, and can see past chat
- I can paste links to issues and web pages for people to test things
- people can reply from their mobile device (mobile friendly)
- I can easily invite people to it or people can easily register on it

What would you suggest?

- I just heard about "gitter" , is it good for that purpose?
- Does Github have something like that?